[gtk/wip/otte/for-gtk-3-24] CSS: Handle unknown resolution

[Benjamin Otte <otte src gnome org>]

commit bdb96507bd59daf9f4002ea170dc4c05ed368a3c
Author: Benjamin Otte <otte redhat com>
Date:   Tue Sep 24 22:37:48 2019 +0200

    CSS: Handle unknown resolution
    
    gdk_screen_get_resolution() can return -1 when the resolution is
    unknown. Catch that case and use the default resolution of 96, like in
    every other case.
    
    Fixes #2119

 gtk/gtkcssshorthandpropertyimpl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkcssshorthandpropertyimpl.c b/gtk/gtkcssshorthandpropertyimpl.c
index d46be8bd0d..53465a988c 100644
--- a/gtk/gtkcssshorthandpropertyimpl.c
+++ b/gtk/gtkcssshorthandpropertyimpl.c
@@ -1118,7 +1118,12 @@ unpack_font_description (GtkCssShorthandProperty *shorthand,
       g_value_init (&v, G_TYPE_DOUBLE);
       size = pango_font_description_get_size (description) / PANGO_SCALE;
       if (!pango_font_description_get_size_is_absolute (description))
-        size = size * gdk_screen_get_resolution (gdk_screen_get_default ()) / 72.0;
+        {
+          double dpi = gdk_screen_get_resolution (gdk_screen_get_default ());
+          if (dpi <= 0.0)
+            dpi = 96.0;
+          size = size * dpi / 72.0;
+        }
       g_value_set_double (&v, size);
       prop = _gtk_style_property_lookup ("font-size");
       _gtk_style_property_assign (prop, props, state, &v);